I. Field of the Invention
The invention is generally concerned with a synchronous motor and, more specifically, a self-starting synchronous motor having a defined direction of rotation.
II. Description of the Prior Art
A multitude of synchronous mini-motors with direction determining start are known. The rotor of such motors is a polarized, permanent magnet rotor, while the stator, which is of the claw-pole type, is equipped with groups of main poles and auxiliary poles with a number of poles which could be different or the same. These main poles and auxiliary poles are shaped with axially located pole lugs from stator pole sheets which are located on both front sides and, further, the auxiliary poles on each frontal side of the stator are equipped with short-circuit discs. In addition, certain main poles or even auxiliary poles form a magnetic shunt. A known synchronous motor of this type (DE-PS No. 12 93 324) is characterized with reference to the above in such a way that a magnetic shunt is provided at all of the inner pole prongs of the main pole groups of a stator pole sheet such that a reduced magnetic flux is provided at the operating air slots of the main pole groups by means of the formation of this shunt. The number of the main poles of this known synchronous motor equals the number of the auxiliary poles. Since the necessary magnetic flux of the same strength in the main poles and in the auxiliary poles is achieved by means of a reduction of the magnetic flux in the main poles, a part of the generated, magnetic flux is lost and remains inactive for the operation of the synchronous motor. The efficiency of this type of synchronous motor is therefore reduced by at least this amount of the inactive flux of the main pole groups. A compensation effect and a balancing effect which are achieved by means of a shunt will always therefore result in the mentioned reduction of the efficiency of the motor.
There is also known a mini-synchronous motor with permanent magnet rotor and a cage-like, ring-shaped closed stator (DE-AS No. 19 23 586), which in turn is based on the known claw-pole construction and which is equipped with auxiliary poles which are loaded by means of short circuiting discs. This synchronous motor is characterized mainly in such a way that only one group each of main poles and auxiliary poles is provided which are located approximately diametrically opposite each other and which extend approximately over one-half of the stator pole circumference and where the rotor is offset eccentrically towards and in the direction of the auxiliary pole group. This is based on the knowledge that in order to achieve a strong direction determining starting torque, the rotary field must be of such a type that the vectorial recording during one complete cycle of the alternating current, that is, during 360.degree., should show a circular shape, if possible, due to the eccentric rotor bearing in relation to the main poles and auxiliary poles which are located on a common cylindrical area. Further, an enlarged air slot is given at the main poles and therefore a reduction of the efficiency as a function of the magnitude of the eccentricity is accepted.
Furthermore, a known synchronous motor with a permanent magnetic rotor should also still be mentioned which is self-starting in its direction (DE-AS No. 11 28 546). This type of synchronous motor has a different number of main poles of different polarity such that the number of main poles is smaller than the number of auxiliary poles and wherein the auxiliary poles are shifted in the direction of rotation with reference to the preceding main poles of equal polarity. In case of a specific version, one-half of the stator of the synchronous motor is equipped with six main poles and six auxiliary poles of equal polarity and the other half of the stator with four main poles and six auxiliary poles of opposite polarity. If the problem is solved in such a way that the flux through the auxiliary poles is made equal to the flux through the main poles such that only the number of main poles of one polarity is reduced, this has the disadvantage that the rotor is loaded axially in such a way that it has the tendency to continuously change its axial position with the operating frequency, which results in an unpleasantly high operating noise level which cannot be permitted for a multitude of applications and which also results in the corresponding wear and tear phenomena.
Furthermore, still another synchronous motor of the type which are of interest in this context should be mentioned in which the sum of all main pole lugs of both stator pole sheets equals the sum of all auxiliary pole lugs, and the total number of the stator lugs is smaller than the rotor pole number (DE-PS No. 20 55 470).
In spite of these known individual measures for the improvement of the operating characteristics and/or the efficiency of synchronous motors, the mentioned state of the art shows that the one or other problem could be solved with certain individual measures; however, these solutions always resulted in other disadvantages.
This is the starting point for the present invention which is based on the objective to improve and further develop a self-starting synchronous motor having a defined direction of rotation, a permanent magnetic rotor and a claw-pole type stator in such a way that the efficiency can be optimized with silent operation and that the synchronous motor is characterized by a rapid start and where, in addition, an unambiguous direction of rotation should be preset.